Transcript 11-2 Day 2

AP STATISTICS
LESSON 11 – 2
(DAY 2)
More Accurate Levels in
The t Procedures
ESSENTIAL QUESTION:
How are degrees of freedom figured more
accurately and what procedures are used to
find two-sample confidence intervals and
significance tests in the calculator?
Objectives:
• To contrast the two methods of
calculating degrees of freedom for twosample t tests.
• To use the calculator to find twosample T tests and intervals.
More Accurate Levels in the
t Procedure
• The two-sample t statistic does not
have a t distribution.
• Moreover, the exact distribution
changes as the unknown population
standard deviations σ1 and σ2 change.
Approximate Distribution of the
Two-sample t statistic
Page 659
t procedures remain the same. The
degree of freedom is the only thing that
changes.
Example 11.13
Page 659
Calcium and Blood Pressure,
continued
Two-sample Inference
Use Technology Toolbox on page 660.
Example 11.14 Page 662
DDT Poisoning
The calculations using the more
complex methods of finding the
degrees of freedom are best used by
the calculator. The difference is rarely
of practical importance.
The Pooled Two-sample Procedures
• Procedures that average use the statistical term
“pooled.”
• Pooled two-sample t procedures is a situation where
the variances of both the samples are assumed to be
the same and the sample sizes are the same. This
rarely happens and the same results will occur with
regular t procedures.
• On the print out from a computer use the unequal
line for variances, degrees of freedom, and
probability.